Why was it necessary for marshlall to take the trouble to explain why navigation should be considered as part of commerce

Which statement best describes evidence of a mulitcultural mix in east africa? a. because of what he learned during his pilgrimage to mecca, mansa musa was able to build a center of islamic scholarship. b. the traders of ghana brought back with them slaves from the mediterranean who taught the ghana rulers about christianity. c. clans were made up of lineages that were descendants of multiple ancestors from different regions of africa. d. swahili became a language made up of words spoken by traders along the coast of the indian ocean.